Inline power (also known as Power over Ethernet (PoE)) is a technology for providing electrical power over a wired telecommunications network from power sourcing equipment (PSE) to a powered device (PD) over a link section. The power may be injected by an endpoint PSE at one end of the link section or by a midspan PSE along a midspan of a link section that is distinctly separate from and between the media dependent interfaces (MDI) to which the ends of the link section are electrically and physically coupled.
PoE is defined in the IEEE (Institute of Electrical and Electronics Engineers, Inc.) Standard 802.3-2005, published Dec. 9, 2005 and entitled “IEEE Standard for Information technology—Telecommunications and information exchange between systems—Local and metropolitan area networks—Specific requirements, Part 3: Carrier Sense Multiple Access with Collision Detection (CSMA/CD) Access Method and Physical Layer Specifications, which is incorporated herein by reference. The IEEE 802.3 standard combines the transmission and reception of Ethernet packets with the transmission and reception of DC-based power over the same set of wires in a single Ethernet cable. The IEEE is currently working on an amendment to the standard, referred to as PoE Plus (IEEE 802.3at), which is expected to extend the 802.3 standard power delivery capability to provide increased power to PDs. Inline power is also available through techniques that are non-IEEE 802.3 standard compliant.
In accordance with the 802.3 standard, a PSE carries out a detection process, and if successful, a classification process. The detection process is performed to detect the presence of a PD at a network port prior to sending power to it and to prevent sending power and causing damage to devices that are non-compliant with the PoE standard. The classification process set forth in 802.3, involves applying a voltage in a classification range to the PD. The PD may use a current source to send a predetermined classification current signal back to the PSE. This classification current signal corresponds to the class of the PD. Following classification, if sufficient power is available at the PSE, the PSE allocates and supplies power to the PD.
While the 802.3 standard delivers different wattages, powered devices are often allocated more power than they need. Furthermore, the IEEE 802.3 standard does not describe how power is managed within a PSE or how a PSE determines actual PD power requirements.
The average power available on a PSE port can be less than the maximum PD power demand. Power is typically allocated based on an assumption that the power requested by the PD matches the real power demand. However, PDs sometimes draw more power than their reported power demand. This may be, for example, due to defective PDs or failure to take into account system cable loss or system component variations when specifying a PD power demand.
It is therefore desirable to provide a method and system for policing inline power to manage power and increase the likelihood that a powered device remains powered on even if one or more powered devices incorrectly reports its peak power requirement.